Final answer:
Mirabeau Buonaparte Lamar's major contribution as the President of Texas was promoting education and allocating public lands for schools and universities.
Step-by-step explanation:
Lamar's Major Contribution to Texas
Lamar's most significant contribution during his presidency was C) Promoting education and public lands.
Mirabeau Buonaparte Lamar, often referred to as the "Father of Texas Education," served as the second President of the Republic of Texas after Sam Houston.
Lamar promoted education by setting aside land for public schools and two universities.
This initiative established a foundation for the educational system and provided long-term benefits to the state.
His presidency did not coincide with Texas’ annexation to the United States, the Texas Declaration of Independence, nor was he directly involved in the Mexican-American War as President of Texas; these events relate to other important figures and times in Texas history.